1. Field of the Invention
The present invention relates to an audio processing apparatus that plays back multichannel audio data.
2. Description of the Related Art
An audio playback system including a BD (Blue-ray disc) player, an AV amplifier, and a display device is used. Audio data transmitted from the BD player to the AV amplifier is generated by encoding multichannel audio data. For example, as illustrated in FIG. 3, the multichannel audio data includes a left audio signal L, a right audio signal R, a central audio signal C, a low-frequency audio signal SW, a surround left audio signal SL, and a surround right audio signal SR. Recently HD (High Definition)-related audio formats, such as Dolby True HD, Dolby Digital Plus, and DTS-HD, which are used in a BD player, appear on the scene. A surround back left audio signal SBL, a surround back right audio signal SBR, a left outside audio signal LW, a right outside audio signal RW, a left upside audio signal LH, and a right upside audio signal RH are further added in the HD-related audio formats.
However, when amplifiers corresponding to the audio signals of all the channels are provided in the AV amplifier, it is necessary to provide the amplifiers for the total of 11.1 channels, which results in a problem in that a cost increases significantly. The same holds true for the case that, as illustrated in FIG. 10, a left-central-side audio signal LC and a right-central-side audio signal RC are added instead of any one of the extended channels (or in addition to the extended channels). The same also holds true for the case that the AV amplifier generates the extended channels in a DSP according to a listening mode.
An audio processing apparatus in FIG. 12 is conceivable for the purpose of solving the problem. According to the audio processing apparatus, in the case that the surround back left audio signal SBL and the left upside audio signal LH are included, the surround back left audio signal SBL is supplied from a DAC 511a to an amplifier 512a, and the left upside audio signal LH is supplied from a DAC 511b to an amplifier 512b. Switches S513a and S513d are controlled in an on state, and switches S513b and S513c are controlled in an off state. Therefore, the surround back left audio signal SBL amplified by the amplifier 512a is supplied to a surround back left SP terminal 514a, and the left upside audio signal LH amplified by the amplifier 512b is supplied to a left upside SP terminal 514c (see Japanese Unexamined Patent Publication No. 2011-229113).
In the case that the surround back left audio signal SBL and the left outside audio signal LW are included, the surround back left audio signal SBL is supplied from the DAC 511a to the amplifier 512a, and the left outside audio signal LW is supplied from the DAC 511b to the amplifier 512b. The switches S513a and S513c are controlled in the on state, and switches S513b and S513d are controlled in the off state. Therefore, the surround back left audio signal SBL amplified by the amplifier 512a is supplied to the surround back left SP terminal 514a, and the left outside audio signal LW amplified by the amplifier 512b is supplied to a left outside SP terminal 514b. The left outside audio signal LW is also output from a pre-out terminal 511d. Accordingly, another amplifier device is connected to the pre-out terminal 511d, and the left outside audio signal LW amplified by another amplifier device can also be played back.
In the case that the left outside audio signal LW and the left upside audio signal LH are included, the left outside audio signal LW is supplied from the DAC 511a to the amplifier 512a, and the left upside audio signal LH is supplied from the DAC 511b to the amplifier 512b. The switches S513b and S513d are controlled in the on state, and the switches S513a and S513c are controlled in the off state. Therefore, the left outside audio signal LW amplified by the amplifier 512a is supplied to the left outside SP terminal 514b, and the left upside audio signal LH amplified by the amplifier 512b is supplied to the left upside SP terminal 514c. The left outside audio signal LW is also output from a pre-out terminal 511c. Accordingly, another amplifier device is connected to the pre-out terminal 511c, and the left outside audio signal LW amplified by another amplifier device can also be played back.
At this point, according to the audio processing apparatus, unfortunately the pre-out terminal that outputs the left outside audio signal LW varies depending on the case that the surround back left audio signal SBL and the left outside audio signal LW are included and the case that the left outside audio signal LW and the left upside audio signal LH are included. That is, it is necessary to change an input terminal of another amplifier, which is connected to the pre-out terminal, according to a combination of channels included in the multichannel audio data.
For example, when an additional DAC is provided to always supply the left outside audio signal LW from the additional DAC to the fixed pre-out terminal, the problem that the pre-out terminal outputting the left outside audio signal LW varies can be solved. However, in the audio processing apparatus, it is necessary to provide the DAC for other uses, such as an output of an HDMI signal of ZONE2, and the number of DACs increases, which results in a problem of a cost increase.